Yesterday I brewed one cup each from two different coffees. I followed Alan's recipe (13.5g finely ground to 115g at 175°F, 10 sec stir, slow press), but I did not dilute the coffee prior to tasting.

The first was Hoja Verde, a dark roasted coffee I brought home mostly just as a souvenir from Quito last November. It was roasted in August 2012 and has an expiration date for August 2013. It has been in my freezer since November. I included it because it is dark and it is my understanding that dark roasts have a greater capacity for extraction. This coffee seemed to me about the same as it did in November, which is to say it tasted burnt. But the Adler recipe did not make it any worse. It was not overly bitter. It tasted the way I imagine a charcoal briquette should taste.

The second was Blue Bottle Three Africans, a lighter roasted blend. It was roasted 12 days ago and spent about half of that time in the freezer. I like this coffee and expected it to taste terrible brewed the Adler way. But it didn't. It was quite drinkable in fact. I can't say that I loved it as there was what I can best describe as a sourness that is absent when I brew it with my normal method. But it wasn't terrible and, like the Hoja Verde, did not have the harsh bitterness I associate with overextraction.

One thing that really struck me about these coffees was their clarity. I brew with metal filters a lot and so I'm used to coffee that isn't clean looking. Even paper filtered Aeropress is often a little cloudy. With such a powdery grind I was expecting these brews to be dirty looking. But instead they were very clear, strikingly so.

I am a novice coffee taster so that's it for my notes. Basically these two cups were okay but not amazing.

I brewed another cup of the Blue Bottle this morning with the Adler recipe and this time diluted it appropriately to match the strength of my normal cup. It was close but had a hint of harshness that distracted from my enjoyment. This was just one cup so maybe I bungled something. But even if it were just as good, the effort to hand grind so finely and then then do a dilution step just isn't worth what I estimate to be a $0.10 savings per cup.

The coffee was ground on a Kyocera CM-50 at the tightest setting where the burrs would still turn. The recipe was 13.5g of coffee, 115g of water at 79.5°C, 10 second stir, then a slow gentle press (at least 1 minute) through an AP paper filter. From each cup a 20ml sample was extracted and cooled (sealed) in a refrigerator. The samples were then filtered @ 0.7 microns and 15.8g of each was evaporated in an 102°C oven for 175 minutes, removed from the oven, covered, allowed to cool, then weighed.

(I'm ok with the numbers (otherrwise) I wouldn't still be here. But appreciate the tasting notes.

Some of what Alan is saying is making me consider... When I first had the AP, I was using a whirly grinder and I began grinding right to sticky powder, and I really liked the coffee. The filter made the process really forgiveable regarding the unevenness of the grind and grinding the bejesus out of the beans gave me, mostly, a very very find grind. Since then my family gave me a burr grinder but not a really skookum one. It never gives me anything like the fineness of the mess I was making with the whirly, and I don't find the results as satisfying. I may go hunt out another whirly from the drugstore while I'm saving up for a better grinder.

After your post I tried an experiment with an aluminum block which I had previously machined to hold small samples in hemispherical cavities. I use a drinking straw as a pipette and put some brew directly in the Brix well and some in an aluminum cavity to (rapidly) cool. Then I took a lot of readings and found that the first two identical readings in the Brix well (the level zone 2. above) agreed with the reading of the sample which had rapidly cooled in the aluminum cavity.

So, I think my method of using the first two repeated readings is ok. But I appreciate your directing attention to potential errors due to evaporation and I'll be mindful of this in the future.

(I'm ok with the numbers (otherrwise) I wouldn't still be here. But appreciate the tasting notes.

Some of what Alan is saying is making me consider... When I first had the AP, I was using a whirly grinder and I began grinding right to sticky powder, and I really liked the coffee. The filter made the process really forgiveable regarding the unevenness of the grind and grinding the bejesus out of the beans gave me, mostly, a very very find grind. Since then my family gave me a burr grinder but not a really skookum one. It never gives me anything like the fineness of the mess I was making with the whirly, and I don't find the results as satisfying. I may go hunt out another whirly from the drugstore while I'm saving up for a better grinder.

Regarding extraction percent in general, I'd like to make some comments:

I measure extraction to evaluate various brewing schemes. I find it a valuable measure of brewing methods.

But I've found that it's not helpful to evaluate the tastiness of the brew. Shortly after the introduction of the AeroPress I measured extraction by the laborious process of drying and weighing the spent grounds. (Later I found the much easier process that we use now). At that time I was measuring 15% extraction and believed that this low extraction was the reason why AeroPress brew was less bitter and less acidic. I viewed 15% with pride.

But as time went on, I learned how to better use my own invention. Specifically, I learned the art of pressing gently. Pressing gently permitted me to use finer grinds and to achieve up to 25% extraction, yet the brew tasted just as smooth and sweet.

So, my current thinking is that high extraction is not detrimental to flavor if the brewing temperature and time are not excessive.

I'd like to emphasize that I achieve 25% extraction simply by using a very fine grind. I do not increase the water temperature above 175F nor do anything which departs from our original "right-side-up" instructions.

Assuming I measured correctly, I was able to get the 25% extraction Alan claimed by using his recipe with a dark roasted coffee. With more lightly roasted coffee the extraction, while still high, was a point and half lower.

This extraction discussion started because it was pointed out that the Aeropress is not a very efficient device. Alan noted that his recipe was efficient because it achieved higher yields by technically overextracting but without any harsh, bitter flavors.

The notion of using extraction as a metric for a balanced brew is predicated on at least a couple of caveats. The first is that the grind is consistent. The second is that the brewing temperature is within some nominal range. The reason for these caveats is that the chemicals that are extracted from coffee do not all go into solution at the same rate, and there is a temperature dependence on those rates. If this were not so we would all simply grind fine and extract maximally at the highest available temperature.

It is quite possible, for example, to brew to 20% extraction using a grind that is a mixture of boulders and dust, but it will not be a balanced brew. Similarly one can brew using 200°C steam or room temperature water to achieve 20% extraction, but they will not taste the same.

So what happens when you brew at 175°F?

To quote one well known coffee expert:

Below about 185F, you get a toddy brew, no acids, no bitters, just sweet and malted. In other words,Postum. If you prefer a coffee at that temperature, either change your coffee or change your drink.

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